According to the World Health Organization (WHO), cancer ranged among the four major non-communicable deadly diseases worldwide in 2012. For the same year, colorectal cancer, breast cancer and respiratory tract cancers were listed within the top 10 causes of death in high income countries (www.who.int/mediacentre/factsheets/fs310/en/).
Epidemiology
In 2012, 14.1 million new cancer cases, 32.6 million patients suffering from cancer (within 5 years of diagnosis) and 8.2 million cancer deaths were estimated worldwide (Ferlay et al., 2013; Bray et al., 2013).
Within the groups of brain cancer, leukemia and lung cancer, the present application particularly focuses on glioblastoma (GB), chronic lymphocytic leukemia (CLL), and non-small cell and small cell lung cancer (NSCLC and SCLC).
Lung cancer is the most common type of cancer worldwide and the leading cause of death from cancer in many countries.
Breast cancer is an immunogenic cancer entity and different types of infiltrating immune cells in primary tumors exhibit distinct prognostic and predictive significance. A large number of early phase immunotherapy trials have been conducted in breast cancer patients. Most of the completed vaccination studies targeted HER2 and carbohydrate antigens like MUC-1 and revealed rather disappointing results. Clinical data on the effects of immune checkpoint modulation with ipilimumab and other T cell-activating antibodies in breast cancer patients are emerging (Emens, 2012).
Chronic Lymphocytic Leukemia
While CLL is not curable at present, many patients show only slow progression of the disease or worsening of symptoms. As patients do not benefit from an early onset of treatment, the initial approach is “watch and wait” (Richards et al., 1999). For patients with symptomatic or rapidly progressing disease, several treatment options are available. These include chemotherapy, targeted therapy, immune-based therapies like monoclonal antibodies, chimeric antigen-receptors (CARs) and active immunotherapy, and stem cell transplants.
Monoclonal antibodies are widely used in hematologic malignancies. This is due to the knowledge of suitable antigens based on the good characterization of immune cell surface molecules and the accessibility of tumor cells in blood or bone marrow. Common monoclonal antibodies used in CLL therapy target either CD20 or CD52. Rituximab, the first monoclonal anti-CD20 antibody originally approved by the FDA for treatment of NHLs, is now widely used in CLL therapy. Combinational treatment with rituximab/fludarabine/cyclophosphamide leads to higher CR rates and improved overall survival (OS) compared to the combination fludarabine/cyclophosphamide and has become the preferred treatment option (Hallek et al., 2008). Ofatumomab targets CD20 and is used for therapy of refractory CLL patients (Wierda et al., 2011). Obinutuzumab is another monoclonal anti-CD20 antibody used in first-line treatment in combination with chlorambucil (Goede et al., 2014).
Alemtuzumab is an anti-CD52 antibody used for treatment of patients with chemotherapy-resistant disease or patients with poor prognostic factors as del 17p or p53 mutations (Parikh et al., 2011).
Novel monoclonal antibodies target CD37 (otlertuzumab, BI 836826, IMGN529 and (177)Lu-tetulomab) or CD40 (dacetuzumab and lucatumumab) and are tested in pre-clinical settings (Robak and Robak, 2014).
Several completed and ongoing trials are based on engineered autologous chimeric antigen receptor (CAR)-modified T cells with CD19 specificity (Maus et al., 2014). So far, only the minority of patients showed detectable or persistent CARs. One partial response (PR) and two complete responses (CR) have been detected in the CAR T-cell trials by Porter et al. and Kalos et al. (Kalos et al., 2011; Porter et al., 2011).
Active immunotherapy includes the following strategies: gene therapy, whole modified tumor cell vaccines, DC-based vaccines and tumor associated antigen (TAA)-derived peptide vaccines.
Approaches in gene therapy make use of autologous genetically modified tumor cells. These B-CLL cells are transfected with immuno-(co-)stimulatory genes like IL-2, IL-12, TNF-alpha, GM-CSF, CD80, CD40L, LFA-3 and ICAM-1 to improve antigen presentation and T cell activation (Carballido et al., 2012). While specific T-cell responses and reduction in tumor cells are readily observed, immune responses are only transient.
Several studies have used autologous DCs as antigen presenting cells to elicit anti-tumor responses. DCs have been loaded ex vivo with tumor associated peptides, whole tumor cell lysate and tumor-derived RNA or DNA. Another strategy uses whole tumor cells for fusion with DCs and generation of DC-B-CLL-cell hybrids. Transfected DCs initiated both CD4+ and CD8+ T-cell responses (Muller et al., 2004). Fusion hybrids and DCs loaded with tumor cell lysate or apoptotic bodies increased tumor-specific CD8+ T-cell responses. Patients that showed a clinical response had increased IL-12 serum levels and reduced numbers of Tregs (Palma et al., 2008).
Different approaches use altered tumor cells to initiate or increase CLL-specific immune responses. An example for this strategy is the generation of trioma cells: B-CLL cells are fused to anti-Fc receptor expressing hybridoma cells that have anti-APC specificity. Trioma cells induced CLL-specific T-cell responses in vitro (Kronenberger et al., 2008).
Another strategy makes use of irradiated autologous CLL cells with Bacillus Calmette-Guérin as an adjuvant as a vaccine. Several patients showed a reduction in leukocyte levels or stable disease (Hus et al., 2008).
Besides isolated CLL cells, whole blood from CLL patients has been used as a vaccine after preparation in a blood treatment unit. The vaccine elicited CLL-specific T-cell responses and led to partial clinical responses or stable disease in several patients (Spaner et al., 2005).
Several TAAs are over-expressed in CLL and are suitable for vaccinations. These include fibromodulin (Mayr et al., 2005), RHAMM/CD168 (Giannopoulos et al., 2006), MDM2 (Mayr et al., 2006), hTERT (Counter et al., 1995), the oncofetal antigen-immature laminin receptor protein(OFAiLRP) (Siegel et al., 2003), adipophilin (Schmidt et al., 2004), survivin (Granziero et al., 2001), KW1 to KW14 (Krackhardt et al., 2002) and the tumor-derived IgVHCDR3 region (Harig et al., 2001; Carballido et al., 2012). A phase I clinical trial was conducted using the RHAMM-derived R3 peptide as a vaccine. 5 of 6 patients had detectable R3-specific CD8+ T-cell responses (Giannopoulos et al., 2010).
Colorectal Cancer
Depending on the colorectal cancer (CRC) stage, different standard therapies are available for colon and rectal cancer. Standard procedures include surgery, radiation therapy, chemotherapy and targeted therapy for CRC (Berman et al., 2015a; Berman et al., 2015b).
In addition to chemotherapeutic drugs, several monoclonal antibodies targeting the epidermal growth factor receptor (EGFR, cetuximab, panitumumab) or the vascular endothelial growth factor-A (VEGF-A, bevacizumab) are administered to patients with high stage disease. For second-line and later treatment the inhibitor for VEGF aflibercept, the tyrosine kinase inhibitor regorafenib and the thymidylate-synthetase inhibitor TAS-102 and the dUTPase inhibitor TAS-114 can be used (Stintzing, 2014; Wilson et al., 2014).
The most recent clinical trials analyze active immunotherapy as a treatment option against CRC. Those strategies include the vaccination with peptides from tumor-associated antigens (TAAs), whole tumor cells, dendritic cell (DC) vaccines and viral vectors (Koido et al., 2013). Peptide vaccines have so far been directed against carcinoembryonic antigen (CEA), mucin 1, EGFR, squamous cell carcinoma antigen recognized by T cells 3 (SART3), beta-human chorionic gonadotropin (beta-hCG), Wilms' Tumor antigen 1 (WT1), Survivin-2B, MAGE3, p53, ring finger protein 43 and translocase of the outer mitochondrial membrane 34 (TOMM34), or mutated KRAS. In several phase I and II clinical trials patients showed antigen-specific CTL responses or antibody production. In contrast to immunological responses, many patients did not benefit from peptide vaccines on the clinical level (Koido et al., 2013; Miyagi et al., 2001; Moulton et al., 2002; Okuno et al., 2011).
Dendritic cell vaccines comprise DCs pulsed with either TAA-derived peptides, tumor cell lysates, apoptotic tumor cells, or tumor RNA or DC-tumor cell fusion products. While many patients in phase I/II trials showed specific immunological responses, only the minority had a clinical benefit (Koido et al., 2013).
Whole tumor cell vaccines consist of autologous tumor cells modified to secrete GM-CSF, modified by irradiation or virus-infected, irradiated cells. Most patients showed no clinical benefit in several phase II/III trials (Koido et al., 2013).
Vaccinia virus or replication-defective avian poxvirus encoding CEA as well as B7.1, ICAM-1 and LFA-3 have been used as vehicles in viral vector vaccines in phase I clinical trials. A different study used nonreplicating canarypox virus encoding CEA and B7.1. Besides the induction of CEA-specific T cell responses 40% of patients showed objective clinical responses (Horig et al., 2000; Kaufman et al., 2008).
Esophageal Cancer
The primary treatment strategy for esophageal cancer depends on tumor stage and location, histological type and the medical condition of the patient. Surgery alone is not sufficient, except in a small subgroup of patients with squamous cell carcinoma.
Data on immunotherapeutic approaches in esophageal cancer are scarce, as only a very limited number of early phase clinical trials have been performed. A vaccine consisting of three peptides derived from three different cancer-testis antigens (TTK protein kinase, lymphocyte antigen 6 complex locus K and insulin-like growth factor (IGF)-II mRNA binding protein 3) was administered to patients with advanced esophageal cancer in a phase I trial with moderate results. Intra-tumoral injection of activated T cells after in vitro challenge with autologous malignant cells elicited complete or partial tumor responses in four of eleven patients in a phase I/II study (Toomey et al., 2013).
Gastric Cancer
Gastric cancer (GC) begins in the cells lining the mucosal layer and spreads through the outer layers as it grows. Surgery is the primary treatment and the only curative treatment for gastric cancer. The efficacy of current therapeutic regimens for advanced GC is poor, resulting in low 5-year survival rates. Immunotherapy might be an alternative approach to ameliorate the survival of GC patients. Adoptive transfer of tumor-associated lymphocytes and cytokine induced killer cells, peptide-based vaccines targeting HER2/neu, MAGE-3 or vascular endothelial growth factor receptor 1 and 2 and dendritic cell-based vaccines targeting HER2/neu showed promising results in clinical GC trials. Immune checkpoint inhibition and engineered T cells might represent additional therapeutic options, which is currently evaluated in pre-clinical and clinical studies (Matsueda and Graham, 2014).
Glioblastoma
The therapeutic options for glioblastoma (WHO grade IV) are very limited. According to the guidelines released by the German Society for Neurology the standard therapy in young patients includes resection or biopsy of the tumor, focal radiation therapy and chemotherapy with temozolomide or CCNU/lomustine or a combination of procarbazine with CCNU and vincristine (PCV). In the USA, Canada and Switzerland treatment with bevacizumab (anti-VEGF-antibody) is also approved for relapse therapy (Leitlinien für Diagnostik and Therapie in der Neurologie, 2014).
Different immunotherapeutic approaches are investigated for the treatment of GB, including immune-checkpoint inhibition, vaccination and adoptive transfer of engineered T cells.
Antibodies directed against inhibitory T cell receptors or their ligands were shown to efficiently enhance T cell-mediated anti-tumor immune responses in different cancer types, including melanoma and bladder cancer. The effects of T cell activating antibodies like ipilimumab and nivolumab are therefore assessed in clinical GB trials, but preliminary data indicate autoimmune-related adverse events.
Different vaccination strategies for GB patients are currently investigated, including peptide-based vaccines, heat-shock protein vaccines, autologous tumor cell vaccines, dendritic cell-based vaccines and viral protein-based vaccines. In these approaches peptides derived from GB-associated proteins like epidermal growth factor receptor variant III (EGFRvIII) or heat shock proteins or dendritic cells pulsed with autologous tumor cell lysate or cytomegalo virus components are applied to induce an anti-tumor immune response in GB patients. Several of these studies reveal good safety and tolerability profiles as well as promising efficacy data.
Adoptive transfer of genetically modified T cells is an additional immunotherapeutic approach for the treatment of GB. Different clinical trials currently evaluate the safety and efficacy of chimeric antigen receptor bearing T cells directed against HER2, IL-13 receptor alpha 2 and EGFRvIII (Ampie et al., 2015).
Liver Cancer
Disease management depends on the tumor stage at the time of diagnosis and the overall condition of the liver. If surgery is not a treatment option, different other therapies are available at hand.
Lately, a limited number of immunotherapy trials for HCC have been conducted. Cytokines have been used to activate subsets of immune cells and/or increase the tumor immunogenicity (Reinisch et al., 2002; Sangro et al., 2004). Other trials have focused on the infusion of Tumor-infiltrating lymphocytes or activated peripheral blood lymphocytes (Shi et al., 2004; Takayama et al., 1991; Takayama et al., 2000b).
So far, a small number of therapeutic vaccination trials have been executed. Butterfield et al. conducted two trials using peptides derived from alpha-fetoprotein (AFP) as a vaccine or DCs loaded with AFP peptides ex vivo (Butterfield et al., 2003; Butterfield et al., 2006). In two different studies, autologous dendritic cells (DCs) were pulsed ex vivo with autologous tumor lysate (Lee et al., 2005) or lysate of the hepatoblastoma cell line HepG2 (Palmer et al., 2009). So far, vaccination trials have only shown limited improvements in clinical outcomes.
Melanoma
The standard therapy in melanoma is complete surgical resection with surrounding healthy tissue. If resection is not complete or not possible at all, patients receive primary radiation therapy, which can be combined with interferon-alpha administration in advanced stages (stages IIB/C and IIIA-C).
Enhancing the anti-tumor immune responses appears to be a promising strategy for the treatment of advanced melanoma. In the United States the immune checkpoint inhibitor ipilimumab as well as the BRAF kinase inhibitors vemurafenib and dabrafenib and the MEK inhibitor trametinib are already approved for the treatment of advanced melanoma. Both approaches increase the patient's anti-tumor immunity—ipilimumab directly by reducing T cell inhibition and the kinase inhibitors indirectly by enhancing the expression of melanocyte differentiation antigens. Additional checkpoint inhibitors (nivolumab and lambrolizumab) are currently investigated in clinical studies with first encouraging results. Additionally, different combination therapies targeting the anti-tumor immune response are tested in clinical trials including ipilimumab plus nivolumab, ipilimumab plus a gp100-derived peptide vaccine, ipilimumab plus dacarbazine, ipilimumab plus IL-2 and iplimumab plus GM-CSF (Srivastava and McDermott, 2014).
Several different vaccination approaches have already been evaluated in patients with advanced melanoma. So far, phase III trials revealed rather disappointing results and vaccination strategies clearly need to be improved. Therefore, new clinical trials, like the OncoVEX GM-CSF trial or the DERMA trial, aim at improving clinical efficacy without reducing tolerability (www.cancerresearchuk.org).
Adoptive T cell transfer shows great promise for the treatment of advanced stage melanoma. In vitro expanded autologous tumor infiltrating lymphocytes as well as T cells harboring a high affinity T cell receptor for the cancer-testis antigen NY-ESO-1 had significant beneficial and low toxic effects upon transfer into melanoma patients. Unfortunately, T cells with high affinity T cell receptors for the melanocyte specific antigens MART1 and gp100 and the cancer-testis antigen MAGEA3 induced considerable toxic effects in clinical trials. Thus, adoptive T cell transfer has high therapeutic potential, but safety and tolerability of these treatments needs to be further increased (Phan and Rosenberg, 2013; Hinrichs and Restifo, 2013).
Non-Small Cell Lung Cancer
Treatment options are determined by the type (small cell or non-small cell) and stage of cancer and include surgery, radiation therapy, chemotherapy, and targeted biological therapies such as bevacizumab, erlotinib and gefitinib.
To expand the therapeutic options for NSCLC, different immunotherapeutic approaches have been studied or are still under investigation. While vaccination with L-BLP25 or MAGEA3 failed to demonstrate an vaccine-mediated survival advantage in NSCLC patients, an allogeneic cell line-derived vaccine showed promising results in clinical studies. Additionally, further vaccination trials targeting gangliosides, the epidermal growth factor receptor and several other antigens are currently ongoing. An alternative strategy to enhance the patient's anti-tumor T cell response consists of blocking inhibitory T cell receptors or their ligands with specific antibodies. The therapeutic potential of several of these antibodies, including ipilimumab, nivolumab, pembrolizumab, MPDL3280A and MEDI-4736, in NSCLC is currently evaluated in clinical trials (Reinmuth et al., 2015).
Ovarian Cancer
Surgical resection is the primary therapy in early as well as advanced stage ovarian carcinoma. Surgical removal is followed by systemic chemotherapy with platinum analogs, except for very low grade ovarian cancers (stage IA, grade 1), where post-operative chemotherapy is not indicated.
Immunotherapy appears to be a promising strategy to ameliorate the treatment of ovarian cancer patients, as the presence of pro-inflammatory tumor infiltrating lymphocytes, especially CD8-positive T cells, correlates with good prognosis and T cells specific for tumor-associated antigens can be isolated from cancer tissue.
Therefore, a lot of scientific effort is put into the investigation of different immunotherapies in ovarian cancer. A considerable number of pre-clinical and clinical studies has already been performed and further studies are currently ongoing. Clinical data are available for cytokine therapy, vaccination, monoclonal antibody treatment, adoptive cell transfer and immunomodulation.
Cytokine therapy with interleukin-2, interferon-alpha, interferon-gamma or granulocyte-macrophage colony stimulating factor aims at boosting the patient's own anti-tumor immune response and these treatments have already shown promising results in small study cohorts.
Phase I and II vaccination studies, using single or multiple peptides, derived from several tumor-associated proteins (Her2/neu, NY-ESO-1, p53, Wilms tumor-1) or whole tumor antigens, derived from autologous tumor cells revealed good safety and tolerability profiles, but only low to moderate clinical effects.
Monoclonal antibodies that specifically recognize tumor-associated proteins are thought to enhance immune cell-mediated killing of tumor cells. The anti-CA-125 antibodies oregovomab and abagovomab as well as the anti-EpCAM antibody catumaxomab achieved promising results in phase II and III studies. In contrast, the anti-MUC1 antibody HMFG1 failed to clearly enhance survival in a phase III study.
An alternative approach uses monoclonal antibodies to target and block growth factor and survival receptors on tumor cells. While administration of trastuzumab (anti-HER2/neu antibody) and MOv18 and MORAb-003 (anti-folate receptor alpha antibodies) only conferred limited clinical benefit to ovarian cancer patients, addition of bevacizumab (anti-VEGF antibody) to the standard chemotherapy in advanced ovarian cancer appears to be advantageous.
Adoptive transfer of immune cells achieved heterogeneous results in clinical trials. Adoptive transfer of autologous, in vitro expanded tumor infiltrating T cells was shown to be a promising approach in a pilot trial. In contrast, transfer of T cells harboring a chimeric antigen receptor specific for folate receptor alpha did not induce a significant clinical response in a phase I trial. Dendritic cells pulsed with tumor cell lysate or tumor-associated proteins in vitro were shown to enhance the anti-tumor T cell response upon transfer, but the extent of T cell activation did not correlate with clinical effects. Transfer of natural killer cells caused significant toxicities in a phase II study.
Intrinsic anti-tumor immunity as well as immunotherapy are hampered by an immunosuppressive tumor microenvironment. To overcome this obstacle immunomodulatory drugs, like cyclophosphamide, anti-CD25 antibodies and pegylated liposomal doxorubicin are tested in combination with immunotherapy. Most reliable data are currently available for ipilimumab, an anti-CTLA4 antibody, which enhances T cell activity. Ipilimumab was shown to exert significant anti-tumor effects in ovarian cancer patients (Mantia-Smaldone et al., 2012).
Pancreatic Cancer
Therapeutic options for pancreatic cancer patients are very limited. One major problem for effective treatment is the typically advanced tumor stage at diagnosis. Additionally, pancreatic cancer is rather resistant to chemotherapeutics, which might be caused by the dense and hypovascular desmoplastic tumor stroma.
According to the guidelines released by the German Cancer Society, the German Cancer Aid and the Association of the Scientific Medical Societies in Germany, resection of the tumor is the only available curative treatment option.
Vaccination strategies are investigated as further innovative and promising alternative for the treatment of pancreatic cancer. Peptide-based vaccines targeting KRAS mutations, reactive telomerase, gastrin, survivin, CEA and MUC1 have already been evaluated in clinical trials, partially with promising results. Furthermore, clinical trials for dendritic cell-based vaccines, allogeneic GM-CSF-secreting vaccines and algenpantucel-L in pancreatic cancer patients also revealed beneficial effects of immunotherapy. Additional clinical trials further investigating the efficiency of different vaccination protocols are currently ongoing (Salman et al., 2013).
Prostate Cancer
The therapeutic strategy for prostate cancer mainly depends on the cancer stage. The dendritic cell-based vaccine sipuleucel-T was the first anti-cancer vaccine to be approved by the FDA. Due to its positive effect on survival in patients with CRPC, much effort is put into the development of further immunotherapies. Regarding vaccination strategies, the peptide vaccine prostate-specific antigen (PSA)-TRICOM, the personalized peptide vaccine PPV, the DNA vaccine pTVG-HP and the whole cell vaccine expressing GM-CSF GVAX showed promising results in different clinical trials. Furthermore, dendritic cell-based vaccines other than sipuleucel-T, namely BPX-101 and DCVAC/Pa were shown to elicited clinical responses in prostate cancer patients. Immune checkpoint inhibitors like ipilimumab and nivolumab are currently evaluated in clinical studies as monotherapy as well as in combination with other treatments, including androgen deprivation therapy, local radiation therapy, PSA-TRICOM and GVAX. The immunomodulatory substance tasquinimod, which significantly slowed progression and increased progression free survival in a phase II trial, is currently further investigated in a phase III trial. Lenalidomide, another immunomodulator, induced promising effects in early phase clinical studies, but failed to improve survival in a phase III trial. Despite these disappointing results further lenalidomide trials are ongoing (Quinn et al., 2015).
Renal Cell Carcinoma
Initial treatment is most commonly either partial or complete removal of the affected kidney(s) and remains the mainstay of curative treatment (Rini et al., 2008). The known immunogenity of RCC has represented the basis supporting the use of immunotherapy and cancer vaccines in advanced RCC. The interesting correlation between lymphocytes PD-1 expression and RCC advanced stage, grade and prognosis, as well as the selective PD-L1 expression by RCC tumor cells and its potential association with worse clinical outcomes, have led to the development of new anti PD-1/PD-L1 agents, alone or in combination with anti-angiogenic drugs or other immunotherapeutic approaches, for the treatment of RCC (Massari et al., 2015). In advanced RCC, a phase III cancer vaccine trial called TRIST study evaluates whether TroVax (a vaccine using a tumor-associated antigen, 5T4, with a pox virus vector), added to first-line standard of care therapy, prolongs survival of patients with locally advanced or mRCC. Median survival had not been reached in either group with 399 patients (54%) remaining on study however analysis of the data confirms prior clinical results, demonstrating that TroVax is both immunologically active and that there is a correlation between the strength of the 5T4-specific antibody response and improved survival. Further there are several studies searching for peptide vaccines using epitopes being over-expressed in RCC.
Various approaches of tumor vaccines have been under investigation. Studies using whole-tumor approaches, including tumor cell lysates, fusions of dendritic cells with tumor cells, or whole-tumor RNA were done in RCC patients, and remissions of tumor lesions were reported in some of these trials (Avigan et al., 2004; Holtl et al., 2002; Marten et al., 2002; Su et al., 2003; Wittig et al., 2001).
Small Cell Lung Cancer
The treatment and prognosis of SCLC depend strongly on the diagnosed cancer stage. Immune therapy presents an excessively investigated field of cancer therapy. Various approaches are studded in the treatment of SCLC. One of the approaches targets the blocking of CTLA-4, a natural human immune suppressor. The inhibition of CTLA-4 intends to boost the immune system to combat the cancer. Recently, the development of promising immune check point inhibitors for treatment of SCLC has been started. Another approach is based on anti-cancer vaccines which is currently available for treatment of SCLC in clinical studies (American Cancer Society, 2015; National Cancer Institute, 2015).
Acute Myeloid Leukemia
One treatment option for AML is targeting CD33 with antibody-drug conjugates (anti-CD33+calechiamicin, SGN-CD33a, anti-CD33+actinium-225), bispecific antibodies (recognition of CD33+CD3 (AMG 330) or CD33+CD16) and chimeric antigen receptors (CARs) (Estey, 2014).
Non-Hodgkin Lymphoma
Treatment of NHL depends on the histologic type and stage (National Cancer Institute, 2015): Spontaneous tumor regression can be observed in lymphoma patients. Therefore, active immunotherapy is a therapy option (Palomba, 2012).
An important vaccination option includes Id vaccines. B lymphocytes express surface immunoglobulins with a specific amino acid sequence in the variable regions of their heavy and light chains, unique to each cell clone (=idiotype, Id). The idiotype functions as a tumor associated antigen.
Passive immunization includes the injection of recombinant murine anti-Id monoclonal antibodies alone or in combination with IFNalpha, IL2 or chlorambucil.
Active immunization includes the injection of recombinant protein (Id) conjugated to an adjuvant (KLH), given together with GM-CSF as an immune adjuvant. Tumor-specific Id is produced by hybridoma cultures or using recombinant DNA technology (plasmids) by bacterial, insect or mammalian cell culture.
Three phase III clinical trials have been conducted (Biovest, Genitope, Favrille). In two trials patients had received rituximab. GM-CSF was administered in all three trials. Biovest used hybridoma-produced protein, Genitope and Favrille used recombinant protein. In all three trials Id was conjugated to KLH. Only Biovest had a significant result.
Vaccines other than Id include the cancer-testis antigens MAGE, NY-ESO1 and PASD-1, the B-cell antigen CD20 or cellular vaccines. The latest mentioned consist of DCs pulsed with apoptotic tumor cells, tumor cell lysate, DC-tumor cell fusion or DCs pulsed with tumor-derived RNA.
In situ vaccination involves the vaccination with intra-tumoral CpG in combination with chemotherapy or irradiated tumor cells grown in the presence of GM-CSF and collection/expansion/re-infusion of T cells.
Vaccination with antibodies that alter immunologic checkpoints are comprised of anti-CD40, anti-OX40, anti-41 BB, anti-CD27, anti-GITR (agonist antibodies that directly enhance anti-tumor response) or anti-PD1, anti-CTLA-4 (blocking antibodies that inhibit the checkpoint that would hinder the immune response). Examples are ipilimumab (anti-CTLA-4) and CT-011 (anti-PD1) (Palomba, 2012).
Uterine Cancer
Treatment of endometrial carcinomas is stage-dependent. The majority of endometrical carcinomas comprises of well to moderately differentiated endometrioid adenocarcinomas which are usually confined to the corpus uteri at diagnosis and can be cured by hysterectomy (World Cancer Report, 2014).
Also therapies for cervical cancer depend on the stage. In early stages, excision is the standard therapy which might be combined with radio-(chemo-)therapy. Primary radio-(chemo-)therapy is chosen at late stages (Stage III and higher), in cases with lymph node infiltration or in cases in which the tumor can not be excised.
There are also some immunotherapeutic approaches that are currently being tested. In a Phase I/II Clinical Trial patients suffering from uterine cancer were vaccinated with autologous dendritic cells (DCs) electroporated with Wilms' tumor gene 1 (WT1) mRNA. Besides one case of local allergic reaction to the adjuvant, no adverse side effects were observed and 3 out of 6 patients showed an immunological response (Coosemans et al., 2013).
As stated above, HPV infections provoke lesions that may ultimately lead to cervical cancer. Therefore, the HPV viral oncoproteins E6 and E7 that are are constitutively expressed in high-grade lesions and cancer and are required for the onset and maintenance of the malignant phenotype are considered promising targets for immunotherapeutic approaches (Hung et al., 2008; Vici et al., 2014). One study performed Adoptive T-cell therapy (ACT) in patients with metastatic cervical cancer. Patients receive an infusion with E6 and E7 reactive tumor-infiltrating T cells (TILs) resulting in complete regression in 2 and a patial response in 1 out of 9 patients (Stevanovic et al., 2015). Furthermore, an intracellular antibody targeting E7 was reported to block tumor groth in mice (Accardi et al., 2014). Also peptide, DNA and DC-based vaccines targing HPV E6 and E7 are in clinical trials (Vici et al., 2014).
Gallbladder Adenocarcinoma and Cholangiocarcinoma
Cholangiocarcinoma is mostly identified in advanced stages because it is difficult to diagnose. Cholangiocarcinoma is difficult to treat and is usually lethal.
Gallbladder cancer is the most common and aggressive malignancy of the biliary tract worldwide.
Urinary Bladder Cancer
The standard treatment for bladder cancer includes surgery, radiation therapy, chemotherapy and immunotherapy.
At stage 0 and 1, the bladder cancer is typically treated by transurethral resection potentially followed by intravesical chemotherapy and optionally combined with intravesical immunotherapeutic treatment with BCG (bacillus Calmette-Guérin).
An effective immunotherapeutic approach is established in the treatment of aggressive non-muscle invasive bladder cancer (NMIBC). Thereby, a weakened form of the bacterium Mycobacterium bovis (bacillus Calmette-Guérin=BCG) is applied as an intravesical solution. The major effect of BCG treatment is a significant long-term (up to 10 years) protection from cancer recurrence and reduced progression rate. In principle, the treatment with BCG induces a local inflammatory response which stimulates the cellular immune response. The immune response to BCG is based on the following key steps: infection of urothelial and bladder cancer cells by BCG, followed by increased expression of antigen-presenting molecules, induction of immune response mediated via cytokine release, induction of antitumor activity via involvement of various immune cells (thereunder cytotoxic T lymphocytes, neutrophils, natural killer cells, and macrophages) (Fuge et al., 2015; Gandhi et al., 2013).
BCG treatment is in general well tolerated by patients but can be fatal especially by the immunocompromised patients. BCG refractory is observed in about 30-40% of patients (Fuge et al., 2015; Steinberg et al., 2016a). The treatment of patients who failed the BCG therapy is challenging. The patients who failed the BCG treatment are at high risk for developing of muscle-invasive disease. Radical cystectomy is the preferable treatment option for non-responders (Steinberg et al., 2016b; von Rundstedt and Lerner, 2015). The FDA approved second line therapy of BCG-failed NMIBC for patients who desire the bladder preservation is the chemotherapeutic treatment with valrubicin. A number of other second line therapies are available or being currently under investigation as well, thereunder immunotherapeutic approaches like combined BCG-interferon or BCG-check point inhibitor treatments, pre-BCG transdermal vaccination, treatment with Mycobacterium phlei cell wall-nucleic acid (MCNA) complex, mono- or combination chemotherapy with various agents like mitomycin C, gemcitabine, docetaxel, nab-paclitaxel, epirubicin, mitomycin/gemcitabine, gemcitabine/docetaxel, and device-assisted chemotherapies like thermochemo-, radiochemo-, electromotive or photodynamic therapies (Fuge et al., 2015; Steinberg et al., 2016b; von Rundstedt and Lerner, 2015). Further evaluation of available therapies in clinical trials is still required.
The alternative treatment options for advanced bladder cancer are being investigated in ongoing clinical trials. The current clinical trials focused on the development of molecularly targeted therapies and immunotherapies. The targeted therapies investigate the effects of cancerogenesis related pathway inhibitors (i.e. mTOR, vascular endothelial, fibroblast, or epidermal growth factor receptors, anti-angiogenesis or cell cycle inhibitors) in the treatment of bladder cancer. The development of molecularly targeted therapies remains challenging due to high degree of genetic diversity of bladder cancer. The main focus of the current immunotherapy is the development of checkpoint blockage agents like anti-PD1 monoclonal antibody and adoptive T-cell transfer (Knollman et al., 2015b; Grivas et al., 2015; Jones et al., 2016; Rouanne et al., 2016).
Head and Neck Squamous Cell Carcinoma
Head and neck squamous cell carcinomas (HNSCC) are heterogeneous tumors with differences in epidemiology, etiology and treatment (Economopoulou et al., 2016).
HNSCC is considered an immunosuppressive disease, characterized by the dysregulation of immunocompetent cells and impaired cytokine secretion (Economopoulou et al., 2016). Immunotherapeutic strategies differ between HPV-negative and HPV-positive tumors.
In HPV-positive tumors, the viral oncoproteins E6 and E7 represent good targets, as they are continuously expressed by tumor cells and are essential to maintain the transformation status of HPV-positive cancer cells. Several vaccination therapies are currently under investigation in HPV-positive HNSCC, including DNA vaccines, peptide vaccines and vaccines involving dendritic cells (DCs). Additionally, an ongoing phase II clinical trial investigates the efficacy of lymphodepletion followed by autologous infusion of TILs in patients with HPV-positive tumors (Economopoulou et al., 2016).
In HPV-negative tumors, several immunotherapeutic strategies are currently used and under investigation. The chimeric IgG1 anti-EGFR monoclonal antibody cetuximab has been approved by the FDA in combination with chemotherapy as standard first line treatment for recurring/metastatic HNSCC. Other anti-EGFR monoclonal antibodies, including panitumumab, nimotuzumab and zalutumumab, are evaluated in HNSCC. Several immune checkpoint inhibitors are investigated in clinical trials for their use in HNSCC. They include the following antibodies: Ipilimumab (anti-CTLA-4), tremelimumab (anti-CTLA-4), pembrolizumab (anti-PD-1), nivolumab (anti-PD-1), durvalumab (anti-PD-1), anti-KIR, urelumab (anti-CD137), and anti-LAG-3.
Two clinical studies with HNSCC patients evaluated the use of DCs loaded with p53 peptides or apoptotic tumor cells. The immunological responses were satisfactory and side effects were acceptable.
Several studies have been conducted using adoptive T cell therapy (ACT). T cells were induced against either irradiated autologous tumor cells or EBV. Results in disease control and overall survival were promising (Economopoulou et al., 2016).
Considering the severe side-effects and expense associated with treating cancer, there is a need to identify factors that can be used in the treatment of cancer in general and hepatocellular carcinoma (HCC), colorectal carcinoma (CRC), glioblastoma (GB), gastric cancer (GC), esophageal cancer, non-small cell lung cancer (NSCLC), pancreatic cancer (PC), renal cell carcinoma (RCC), benign prostate hyperplasia (BPH), prostate cancer (PCA), ovarian cancer (OC), melanoma, breast cancer, chronic lymphocytic leukemia (CLL), Merkel cell carcinoma (MCC), small cell lung cancer (SCLC), Non-Hodgkin lymphoma (NHL), acute myeloid leukemia (AML), gallbladder cancer and cholangiocarcinoma (GBC, CCC), urinary bladder cancer (UBC), uterine cancer (UEC), head and neck squamous cell carcinoma (HNSCC), in particular. There is also a need to identify factors representing biomarkers for cancer in general and the above-mentioned cancer types in particular, leading to better diagnosis of cancer, assessment of prognosis, and prediction of treatment success.
Immunotherapy of cancer represents an option of specific targeting of cancer cells while minimizing side effects. Cancer immunotherapy makes use of the existence of tumor associated antigens.
The current classification of tumor associated antigens (TAAs) comprises the following major groups:    a) Cancer-testis antigens: The first TAAs ever identified that can be recognized by T cells belong to this class, which was originally called cancer-testis (CT) antigens because of the expression of its members in histologically different human tumors and, among normal tissues, only in spermatocytes/spermatogonia of testis and, occasionally, in placenta. Since the cells of testis do not express class I and II HLA molecules, these antigens cannot be recognized by T cells in normal tissues and can therefore be considered as immunologically tumor-specific. Well-known examples for CT antigens are the MAGE family members and NY-ESO-1.    b) Differentiation antigens: These TAAs are shared between tumors and the normal tissue from which the tumor arose. Most of the known differentiation antigens are found in melanomas and normal melanocytes. Many of these melanocyte lineage-related proteins are involved in biosynthesis of melanin and are therefore not tumor specific but nevertheless are widely used for cancer immunotherapy. Examples include, but are not limited to, tyrosinase and Melan-A/MART-1 for melanoma or PSA for prostate cancer.    c) Over-expressed TAAs: Genes encoding widely expressed TAAs have been detected in histologically different types of tumors as well as in many normal tissues, generally with lower expression levels. It is possible that many of the epitopes processed and potentially presented by normal tissues are below the threshold level for T-cell recognition, while their over-expression in tumor cells can trigger an anticancer response by breaking previously established tolerance. Prominent examples for this class of TAAs are Her-2/neu, survivin, telomerase, or WT1.    d) Tumor-specific antigens: These unique TAAs arise from mutations of normal genes (such as β-catenin, CDK4, etc.). Some of these molecular changes are associated with neoplastic transformation and/or progression. Tumor-specific antigens are generally able to induce strong immune responses without bearing the risk for autoimmune reactions against normal tissues. On the other hand, these TAAs are in most cases only relevant to the exact tumor on which they were identified and are usually not shared between many individual tumors. Tumor-specificity (or -association) of a peptide may also arise if the peptide originates from a tumor-(-associated) exon in case of proteins with tumor-specific (-associated) isoforms.    e) TAAs arising from abnormal post-translational modifications: Such TAAs may arise from proteins which are neither specific nor overexpressed in tumors but nevertheless become tumor associated by posttranslational processes primarily active in tumors. Examples for this class arise from altered glycosylation patterns leading to novel epitopes in tumors as for MUC1 or events like protein splicing during degradation which may or may not be tumor specific.    f) Oncoviral proteins: These TAAs are viral proteins that may play a critical role in the oncogenic process and, because they are foreign (not of human origin), they can evoke a T-cell response. Examples of such proteins are the human papilloma type 16 virus proteins, E6 and E7, which are expressed in cervical carcinoma.
T-cell based immunotherapy targets peptide epitopes derived from tumor-associated or tumor-specific proteins, which are presented by molecules of the major histocompatibility complex (MHC). The antigens that are recognized by the tumor specific T lymphocytes, that is, the epitopes thereof, can be molecules derived from all protein classes, such as enzymes, receptors, transcription factors, etc. which are expressed and, as compared to unaltered cells of the same origin, usually up-regulated in cells of the respective tumor.
There are two classes of MHC-molecules, MHC class I and MHC class II. MHC class I molecules are composed of an alpha heavy chain and beta-2-microglobulin, MHC class II molecules of an alpha and a beta chain. Their three-dimensional conformation results in a binding groove, which is used for non-covalent interaction with peptides.
MHC class I molecules can be found on most nucleated cells. They present peptides that result from proteolytic cleavage of predominantly endogenous proteins, defective ribosomal products (DRIPs) and larger peptides. However, peptides derived from endosomal compartments or exogenous sources are also frequently found on MHC class I molecules. This non-classical way of class I presentation is referred to as cross-presentation in the literature (Brossart and Bevan, 1997; Rock et al., 1990). MHC class II molecules can be found predominantly on professional antigen presenting cells (APCs), and primarily present peptides of exogenous or transmembrane proteins that are taken up by APCs e.g. during endocytosis, and are subsequently processed.
Complexes of peptide and MHC class I are recognized by CD8-positive T cells bearing the appropriate T-cell receptor (TCR), whereas complexes of peptide and MHC class II molecules are recognized by CD4-positive-helper-T cells bearing the appropriate TCR. It is well known that the TCR, the peptide and the MHC are thereby present in a stoichiometric amount of 1:1:1.
CD4-positive helper T cells play an important role in inducing and sustaining effective responses by CD8-positive cytotoxic T cells. The identification of CD4-positive T-cell epitopes derived from tumor associated antigens (TAA) is of great importance for the development of pharmaceutical products for triggering anti-tumor immune responses (Gnjatic et al., 2003). At the tumor site, T helper cells, support a cytotoxic T cell-(CTL-) friendly cytokine milieu (Mortara et al., 2006) and attract effector cells, e.g. CTLs, natural killer (NK) cells, macrophages, and granulocytes (Hwang et al., 2007).
In the absence of inflammation, expression of MHC class II molecules is mainly restricted to cells of the immune system, especially professional antigen-presenting cells (APC), e.g., monocytes, monocyte-derived cells, macrophages, dendritic cells. In cancer patients, cells of the tumor have been found to express MHC class II molecules (Dengjel et al., 2006).
Elongated peptides of the invention can act as MHC class II active epitopes.
T-helper cells, activated by MHC class II epitopes, play an important role in orchestrating the effector function of CTLs in anti-tumor immunity. T-helper cell epitopes that trigger a T-helper cell response of the TH1 type support effector functions of CD8-positive killer T cells, which include cytotoxic functions directed against tumor cells displaying tumor-associated peptide/MHC complexes on their cell surfaces. In this way tumor-associated T-helper cell peptide epitopes, alone or in combination with other tumor-associated peptides, can serve as active pharmaceutical ingredients of vaccine compositions that stimulate anti-tumor immune responses.
It was shown in mammalian animal models, e.g., mice, that even in the absence of CD8-positive T lymphocytes, CD4-positive T cells are sufficient for inhibiting manifestation of tumors via inhibition of angiogenesis by secretion of interferon-gamma (IFNγ) (Beatty and Paterson, 2001; Mumberg et al., 1999). There is evidence for CD4 T cells as direct anti-tumor effectors (Braumuller et al., 2013; Tran et al., 2014).
Since the constitutive expression of HLA class II molecules is usually limited to immune cells, the possibility of isolating class II peptides directly from primary tumors was previously not considered possible. However, Dengjel et al. were successful in identifying a number of MHC Class II epitopes directly from tumors (WO 2007/028574, EP 1 760 088 B1).
Since both types of response, CD8 and CD4 dependent, contribute jointly and synergistically to the anti-tumor effect, the identification and characterization of tumor-associated antigens recognized by either CD8+ T cells (ligand: MHC class I molecule+peptide epitope) or by CD4-positive T-helper cells (ligand: MHC class II molecule+peptide epitope) is important in the development of tumor vaccines.
For an MHC class I peptide to trigger (elicit) a cellular immune response, it also must bind to an MHC-molecule. This process is dependent on the allele of the MHC-molecule and specific polymorphisms of the amino acid sequence of the peptide. MHC-class-I-binding peptides are usually 8-12 amino acid residues in length and usually contain two conserved residues (“anchors”) in their sequence that interact with the corresponding binding groove of the MHC-molecule. In this way each MHC allele has a “binding motif” determining which peptides can bind specifically to the binding groove.
In the MHC class I dependent immune reaction, peptides not only have to be able to bind to certain MHC class I molecules expressed by tumor cells, they subsequently also have to be recognized by T cells bearing specific T cell receptors (TCR).
For proteins to be recognized by T-lymphocytes as tumor-specific or -associated antigens, and to be used in a therapy, particular prerequisites must be fulfilled. The antigen should be expressed mainly by tumor cells and not, or in comparably small amounts, by normal healthy tissues. In a preferred embodiment, the peptide should be over-presented by tumor cells as compared to normal healthy tissues. It is furthermore desirable that the respective antigen is not only present in a type of tumor, but also in high concentrations (i.e. copy numbers of the respective peptide per cell). Tumor-specific and tumor-associated antigens are often derived from proteins directly involved in transformation of a normal cell to a tumor cell due to their function, e.g. in cell cycle control or suppression of apoptosis. Additionally, downstream targets of the proteins directly causative for a transformation may be up-regulated and thus may be indirectly tumor-associated. Such indirect tumor-associated antigens may also be targets of a vaccination approach (Singh-Jasuja et al., 2004). It is essential that epitopes are present in the amino acid sequence of the antigen, in order to ensure that such a peptide (“immunogenic peptide”), being derived from a tumor associated antigen, leads to an in vitro or in vivo T-cell-response.
Basically, any peptide able to bind an MHC molecule may function as a T-cell epitope. A prerequisite for the induction of an in vitro or in vivo T-cell-response is the presence of a T cell having a corresponding TCR and the absence of immunological tolerance for this particular epitope.
Therefore, TAAs are a starting point for the development of a T cell based therapy including but not limited to tumor vaccines. The methods for identifying and characterizing the TAAs are usually based on the use of T-cells that can be isolated from patients or healthy subjects, or they are based on the generation of differential transcription profiles or differential peptide expression patterns between tumors and normal tissues. However, the identification of genes over-expressed in tumor tissues or human tumor cell lines, or selectively expressed in such tissues or cell lines, does not provide precise information as to the use of the antigens being transcribed from these genes in an immune therapy. This is because only an individual subpopulation of epitopes of these antigens are suitable for such an application since a T cell with a corresponding TCR has to be present and the immunological tolerance for this particular epitope needs to be absent or minimal. In a very preferred embodiment of the invention it is therefore important to select only those over- or selectively presented peptides against which a functional and/or a proliferating T cell can be found. Such a functional T cell is defined as a T cell, which upon stimulation with a specific antigen can be clonally expanded and is able to execute effector functions (“effector T cell”).
In case of targeting peptide-MHC by specific TCRs (e.g. soluble TCRs) and antibodies or other binding molecules (scaffolds) according to the invention, the immunogenicity of the underlying peptides is secondary. In these cases, the presentation is the determining factor.